The present invention relates to floating docks with variable buoyancy.
Floating drive on dry docks are known in the art. One such dock is shown in U.S. Pat. No. 5,931,113. That dock is assembled from a number of flotation units which are airtight. These flotation units come in two sizes, so-called full cubes and half cubes. Through selective arrangement of these units in a single layer a wide variety of watercraft can be accommodated.
As disclosed in U.S. Pat. No. 5,931,113, some watercraft, especially larger, heavier craft, require more buoyancy, particularly in the aft region of the dock, than a single layer of flotation units can provide in order for the dock to satisfactorily support the craft out of the water. The required buoyancy can be provided by one or more additional rows of floatation units placed on their sides to form a supporting beam. This beam, fastened at its outboard ends to the upper layer of flotation units, provides the added lift necessary for such heavier boats. In addition to providing lift, the beam illustrated in U.S. Pat. No. 5,931,113 provides stiffness across the width of the dock.
The floating drive on dry dock of the type illustrated in U.S. Pat No. 5,931,113 relies on flexible joints between the flotation units to enable a watercraft to drive onto the dock. At the start of the drive on operation the craft presses down against the aft end of the dock while the forward end of the dock remains essentially flat upon the water. In side elevation view, the aft end of the dock curves downward, forming a ramp for the boat to be driven on.
As the boat moves up the ramp and onto the dock, the dock flattens out and the entire boat is lifted out of the water. In addition, the ""113 patent suggests that a beam with variable buoyancy may be used. An air compressor can be used to feed air through a manifold to the floatation units, and the buoyancy of the beam can be adjusted with each use. Experience has shown that such a system may not lift evenly and under uneven loads it may also list to one side or the other, and fail to return to a flat trim.
The present invention provides a floating drive on dry dock formed of flotation cells and including a group of flotation cells that may be selectively filled with air to increase their buoyancy after a boat has been driven onto the dock. The invention further provides a system for supplying air through a manifold to each of the adjustable buoyancy cells and for limiting movement of air between cells when a load is applied to them unevenly. These results are achieved by assuring that air flows into the cells more or less evenly, and by back filling the manifold with water after the cells have been inflated to the desired degree of buoyancy.